Oguchi Onyewu has successfully returned from his injury layoff, and could be a valuable piece in Sporting's back line on Thursday when they try to hang onto their narrow lead at Athletic Bilbao.

Despite conceding the opening goal to their guests last Thursday, Sporting fought back to take the upper hand with a pair of late scores in Lisbon for the 2-1 first-leg advantage, and will need to put in a similar gutsy performance should they hope to reach next month's final in Bucharest.

The early away goal by Bilbao will put them under considerable pressure to score, as even a narrow 1-0 shut-out win by Marcelo Bielsa's squad would push Onyewu and his teammates out of the competition.

Fortunately for the team, they are on perhaps their best run of the season, having gone undefeated over their last seven games in all competitions, including a gutsy 3-2 win over fifth-place Funchal that left them with a slight hope of achieving Champions League qualification.

Onyewu played the full 90 minutes in that game for his first return to action in months, and could very well feature in the starting lineup again in Spain.

In a similar fashion Bilbao are putting the final touches on a strong season in Spain's La Liga, and have thin hopes of making up the four-point gap keeping them from the final Champions League spot over their final four league games.

They beat Racing Santander by the narrowest of margins over the weekend, and aside from the first-leg loss to their Portuguese counterparts, and undefeated in their last five overall.

Sporting are looking to break their jinx in Spain, having failed to win in the previous nine trips to their neighbors. Athletic, conversely, have won on all three occasions when they have hosted Portuguese opposition.

Should the Portuguese manage to hold on to the lead, they would face another Spanish team in the final, with Valencia and Atletico Madrid set to contest their second leg at Valencia also on Thursday.

Both teams will have nearly full squads to choose from. Sporting do see the return of Chilean midfielder Matias Fernandez from a two-game suspension, however midfielder Fito Rinaudo and defender Alberto Rodriguez will both be absent from the bench due to injuries.

Bilbao are only missing all-rounder Oscar de Marcos, as the player responsible for two of their goals in the earlier two-legged upset over Manchester United is suspended.